Avoid OOB index when fixing constant array-initialization (microsoft#6825)

If the index on a constant store into an array is negative or out of
bounds, that's an error, but shouldn't make the compiler index a vector
out of bounds.

Fixed: microsoft#6824

Author: dneto0

lib/Transforms/Scalar/DxilFixConstArrayInitializer.cpp

@@ -119,6 +119,10 @@ static bool TryFixGlobalVariable(
 
     GEPOperator *GEP = cast<GEPOperator>(Store->getPointerOperand());
     uint64_t Index = cast<ConstantInt>(GEP->getOperand(2))->getLimitedValue();
+    if (Index >= LatestStores.size()) {
+      // Skip out of bounds index.
+      continue;
+    }
 
     if (LatestStores[Index] <= StoreIndex) {
       InitValue[Index] = cast<Constant>(Store->getValueOperand());
@@ -182,4 +186,4 @@ Pass *llvm::createDxilFixConstArrayInitializerPass() {
 }
 
 INITIALIZE_PASS(DxilFixConstArrayInitializer, "dxil-fix-array-init",
-                "Dxil Fix Array Initializer", false, false)
+                "Dxil Fix Array Initializer", false, false)

tools/clang/test/DXC/Passes/DxilFixConstArrayInitializer/negative-index.ll

@@ -0,0 +1,74 @@
+; RUN: %dxopt %s -hlsl-passes-resume -dxil-fix-array-init -S | FileCheck %s
+
+; The pass should not perform an out of bounds access when trying to determine
+; which elements of an array are coverd by stores.
+; The store instructions may have out of bounds accesses, including to negative
+; indices.  In these cases, ignore those stores.  They are undefined behaviour
+; anyway, and the best thing to do with them in this pass is nothing.
+; If the original HLSL code used a literal -1 for the array index, the program
+; is rejected at an earlier stage of compilation.
+
+; Issue: #6824
+
+; Original HLSL:
+
+; groupshared float4 w;
+;
+; [numthreads(1, 1, 1)]
+; void b() {
+;   int i = -1;
+;   w[i] = 0;
+; }
+
+; Check that the store instruction remains, and the compiler does not crash.
+
+; CHECK: define void @b
+; CHECK: store float 0
+; CHECK-SAME: , i32 0, i32 -1)
+; CHECK-NEXT: ret void
+
+target datalayout = "e-m:e-p:32:32-i1:32-i8:32-i16:32-i32:32-i64:64-f16:32-f32:32-f64:64-n8:16:32:64"
+target triple = "dxil-ms-dx"
+
+@"\01?w@@3V?$vector@M$03@@A.v" = addrspace(3) global [4 x float] undef, align 4
+
+; Function Attrs: nounwind
+define void @b() #0 {
+entry:
+  store float 0.000000e+00, float addrspace(3)* getelementptr inbounds ([4 x float], [4 x float] addrspace(3)* @"\01?w@@3V?$vector@M$03@@A.v", i32 0, i32 -1), !dbg !13, !tbaa !17 ; line:6 col:8
+  ret void, !dbg !21 ; line:7 col:1
+}
+
+attributes #0 = { nounwind }
+
+!llvm.module.flags = !{!0}
+!pauseresume = !{!1}
+!llvm.ident = !{!2}
+!dx.version = !{!3}
+!dx.valver = !{!4}
+!dx.shaderModel = !{!5}
+!dx.typeAnnotations = !{!6}
+!dx.entryPoints = !{!10}
+
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = !{!"hlsl-dxilemit", !"hlsl-dxilload"}
+!2 = !{!"dxc(private) 1.8.0.4640 (issue-785, 45018c752d)"}
+!3 = !{i32 1, i32 0}
+!4 = !{i32 1, i32 8}
+!5 = !{!"cs", i32 6, i32 0}
+!6 = !{i32 1, void ()* @b, !7}
+!7 = !{!8}
+!8 = !{i32 1, !9, !9}
+!9 = !{}
+!10 = !{void ()* @b, !"b", null, null, !11}
+!11 = !{i32 4, !12}
+!12 = !{i32 1, i32 1, i32 1}
+!13 = !DILocation(line: 6, column: 8, scope: !14)
+!14 = !DISubprogram(name: "b", scope: !15, file: !15, line: 4, type: !16, isLocal: false, isDefinition: true, scopeLine: 4, flags: DIFlagPrototyped, isOptimized: false, function: void ()* @b)
+!15 = !DIFile(filename: "a.hlsl", directory: "")
+!16 = !DISubroutineType(types: !9)
+!17 = !{!18, !18, i64 0}
+!18 = !{!"float", !19, i64 0}
+!19 = !{!"omnipotent char", !20, i64 0}
+!20 = !{!"Simple C/C++ TBAA"}
+!21 = !DILocation(line: 7, column: 1, scope: !14)